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Before you write the boiler off as dead, let's run through the checks I'd do first — most take under a minute each.
No hot water at all — where do I start? Check the boiler's pressure gauge first, then confirm the thermostat and timer are actually calling for heat, then check for a tripped switch at the boiler and at your consumer unit. If all three check out and you're still cold, ring 020 4577 2888 and I'll put you through to a local plumber. Smell gas instead? Leave the house and call 0800 111 999.
Below about 1 bar cold, and the boiler often won't fire properly at all. Top it up once through the filling loop, following your manual.
This is always where I'd start, because low pressure is such a common cause of a boiler that's simply gone quiet rather than actually broken. Find the gauge on the front of the unit — most sealed systems want to sit around 1 to 1.5 bar when cold, and your manual will give the precise range for your model. If it's sitting noticeably below that, the filling loop lets you bring it back up yourself, slowly, watching the needle as you go.
If topping it up brings the hot water straight back, that's good news for tonight but worth keeping an eye on. A boiler that needed topping up once isn't a crisis; one that needs it every few weeks is losing water somewhere, and that's worth me having a proper look at rather than you refilling it forever.
Check the programmer's actually set to "on" for hot water, and the thermostat isn't turned right down. A knocked dial or a reset clock catches more people than you'd think.
It sounds almost too simple to mention, but I've arrived at more than a few houses where a knocked programmer or a clock reset after a power cut had quietly switched the hot water schedule off, or a thermostat had been nudged down by a child, a cat, or a hoover cable. Walk over and actually look at the display rather than assuming it's set the way it always is.
While you're there, check whether the system's asking for heating as well as hot water, or just one of the two — that tells me something useful over the phone. A combi boiler that heats radiators fine but won't give hot water, or the reverse, points me towards a different part of the system before I've even picked up my tools.
A fused spur or a tripped RCD can silence a boiler completely, with nothing wrong with the boiler itself. Two minutes of checking, and it might be that simple.
Boilers usually run off a fused spur near the unit, sometimes with its own small switch and indicator light — check that's actually on. Then head to your consumer unit and look for a tripped switch among the row of them; a recent storm, a faulty appliance elsewhere in the house, or simple bad luck can trip a circuit that happens to include the boiler, and everything else on that circuit will usually be dark too, which is your clue.
If resetting a trip switch trips it again immediately, stop there and don't keep flicking it — that's telling you there's a fault on the circuit, not a one-off blip, and it's worth an electrician's eye as much as mine.
If your tank has one, the immersion heater can get you hot water even with the boiler completely down. A dedicated switch, usually marked, and often near the airing cupboard.
Not every home has one — combi boilers heat water on demand and skip the tank entirely — but if you've got a hot water cylinder, there's likely an immersion heater built into it as a backup, original to the house or fitted later. Its switch is usually near the airing cupboard or the cylinder itself, sometimes clearly labelled, sometimes not.
Switching it on won't fix the boiler, but it buys you a tank of hot water for washing and dishes while you wait, which matters more than it sounds like on a cold evening. It draws a fair bit of electricity running for any length of time, so it's a bridge, not a long-term answer, but it's a genuinely useful one to know about.
One reset is a fair try; several in a row rarely help and can mask the actual fault code I need to see. If it locks out again after a single reset, note whatever code or light pattern shows and call me rather than keep cycling the button. That code is often the quickest route to a fix.
That points away from the boiler entirely and towards that one tap or the pipe feeding it — a stuck mixer cartridge, a partially closed isolation valve, or, in cold weather, a frozen short run of pipe to that specific outlet. It's a smaller, cheaper problem than a boiler fault, which is genuinely good news.
Rarely in the urgent, act-now sense — nobody's flooding and nothing's getting worse by the hour. But if it's midwinter, there are elderly residents or young children in the house, or it's been more than a day or two, I'd treat it as worth a same-day call rather than something to leave indefinitely.
Leave the property, don't touch switches or flames, and call the National Gas Emergency Service on 0800 111 999 once safely outside. Not a plumber, not me — that number, first, every single time. Only go back inside once you've been told it's safe.
The main page — how the line works and the areas it covers.
Go to home →The first five minutes, in the right order.
Walk through it →Pressure drops, no heat, error codes — and gas safety.
Walk through it →What to try yourself and when it's the sewer, not your drain.
Walk through it →Honest ballparks and the questions to ask before work starts.
Walk through it →Thawing safely with gentle heat — and the lagging that prevents it.
Walk through it →Damp patches, dropping pressure and the stopcock test.
Walk through it →Ring any hour and I'll put you through to a local plumber covering Armagh and the surrounding villages.
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